Status

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Kafka Connect does not provide an out-of-the-box facility to change log levels. When debugging connectors or the Connect framework, users have to update the log4j.properties file and restart the worker to see new logs. This is cumbersome in most cases, and restarting the worker sometimes hides bugs by resetting the internal state.

Proposed Changes

This change will introduce an /admin/loggers endpoint to the Connect worker. In addition, a new configuration property admin.listeners will be provided to specify which listener to use for the /admin endpoint. The /admin/loggers endpoint will support the following operations:

Public Interfaces

A /admin endpoint that can be configured to be attached to a different listener than the existing Connect endpoints.

The /admin/loggers endpoint that be used to modify log levels.

A new configuration property in WorkerConfig to enable/disable the /admin endpoint along with optionally configuring any HTTPS listeners if needed.

Log level changes are not persisted across worker restarts. These changes also only apply to the worker that receives the PUT request described above.

Compatibility, Deprecation, and Migration Plan

This is a new feature. Existing features will not be changed.

It must be noted that the changes proposed only work when log4j 1.x is used to log messages and is available on classpath. This is the current default in the AK distribution as well. Other loggers (logback, log4j2 etc) will not be supported and this feature (and others mentioned below in related work) will have to be reworked to support these frameworks.

Rejected Alternatives

Changing log levels in a single node of an application will affect other nodes in the cluster (for example, changing log level of a class in one Connect worker will update levels in all workers in a Connect cluster) and this new level will be persisted across node restarts. This is beyond the scope of this proposal.

Using JMX to change log levels is too cumbersome, difficult to secure and the other components are going to move away from it (look at KIP-412 where brokers are now using Admin Client to change log levels).